The present invention relates to a color cathode ray tube apparatus, and more particularly to a color cathode ray tube apparatus that has a high-resolution electron gun.
Most color cathode ray tubes have a panel 1 and a funnel 2 that is formed integral with the panel 1, as is illustrated in FIG. 1. A phosphor screen 3 is provided as a target, opposing the inner surface of the panel 1. The phosphor screen 3 has a number of tricolor segments, each consisting of three stripes or dots of different colors. A shadow mask 4 having a number of apertures is provided, opposing the inner surface of the phosphor screen 3. The funnel 2 has a neck 5, in which an electron gun assembly 7 is arranged. The electron gun assembly 7 is designed to emit three electron beams 6B, 6G and 6R. A deflection yoke 8 is provided outside the funnel 2. The yoke 8 generates horizontal and vertical deflection magnetic fields. The magnetic fields deflect the electron beams 6B, 6G and 6R emitted from the assembly 7, in a horizontal direction and a vertical direction. The electron beams 6B, 6G and 6R thus deflected are applied through the shadow mask 4 to the phosphor screen 3. The screen 3 is thereby scanned in both the horizontal direction and the vertical direction. A color image is thereby displayed on the phosphor screen 3.
A so-called inline color cathode ray tube of self-convergence type has been put to practical use. The inline color-receiving tube has an electron gun assembly 7 that emits a center beam 6G and two side beams 6B and 6R, which have their axes extending in the same horizontal plane. The electron gun assembly has a main electron lens including a low-voltage grid and a high-voltage grid, each having three beam-guiding holes. The holes for guiding the side beams 6B and 6R, made in the low-voltage grid are eccentric to the holes for guiding the side beams 6B and 6R, made in the high-voltage grid. Thanks to this specific positioning of beam-guiding holes, the three electron beams are focused at a center part of the phosphor screen 3. Further, the deflection yoke 8 is designed to generate a horizontal deflection magnetic field shaped like a pincushion and a vertical deflection magnetic field shaped like a barrel. The pincushion-shaped magnetic field and the barrel-shaped magnetic field focus the three electron beams 6B, 6G and 6R at any part of the phosphor screen 3.
An electron gun assembly for use in this type of a color cathode ray tube is known. It is called "extended electric-field type," designed in order to improve the focusing of electron beams at any part of the phosphor screen. This electron gun assembly has a main electron lens having a long focal distance and a large aperture. The main electron lens is formed by such a method as is disclosed in Jpn. Pat. Appln. KOKAI Publication Nos. 61-39346 and 61-39347. That is, the focusing grid structure is not composed of only one grid but is comprised of segment grids, and the anode voltage is divided into partial voltages by a resistor arranged in the neck of the color cathode ray tube. The partial voltages, thus obtained, are applied to the segment grids of the focusing grid structure, which achieves moderate distribution of potential.
FIGS. 2A and 2B show an electron gun assembly of the extended electric-field type described above. As shown in FIG. 2A, the electron gun assembly has three cathodes KB, KG and KR, first to fifth grids G1 to G5, an intermediate electrode GM, sixth grid G6 and a convergence cup 90, which are arranged coaxial, in the order they are mentioned. The cathodes KB, KG and KR each incorporate a heater (not shown). The cathodes KB, KG and KR, girds G1 to G6, electrodes GM and convergence cup 90 are supported by and secured to an insulating support (not shown).
As shown in FIG. 2B, a resistor 100 is provided near the electron gun assembly. One end 110 of the resistor 100 is connected to the sixth grid G6. The other end of the resistor 100 is connected to the fifth grid G5. The resistor 100 is connected, at its middle point 120, to the intermediate electrodes GM. The end 110 of the resistor 100 is connected also to a voltage source 131, which applies an operating voltage to the electron gun assembly.
The first grid G1 is a thin-plate electrode and has three small beam-guiding holes. The second grid G2 is also a thin-plate electrode and has three small beam-guiding holes. The third grid G3 comprises a cups-shaped electrode 31 and a plate-shaped electrode 32, which abut on each other. The cup-shaped electrode 31 opposes the second grid G2 and has three beam-guiding holes slightly larger than the beam-guiding holes of the second grid G2. The holes for guiding one side beam, made in the first to third grids G1 to G3, have a common axis. Similarly, the holes for guiding the other side beam, made in these grids G1 to G3, have a common axis. The two side beams, therefore, travel along the common axes of the side beam guiding holes of the first to third girds G1 to G3. The plate-shaped electrode 32 of the third grid G3, which opposes the fourth grid G4, has three beam-guiding holes having a large diameter.
The fourth grid G4 comprises two cup-shaped electrodes, 41 and 42, which abut on each other. The electrodes 41 and 42 each have three beam-guiding holes having a large diameter. The fifth grid G5 comprises two cup-shaped electrodes 51 and 52, a thin-plate electrode 53, and a thick-plate electrode 54. The cup-shaped electrodes 51 and 52 each have three beam-guiding holes having a large diameter. The thin-plate electrode 53 has three beam-guiding holes that are elongated in the inline direction. The thick-plate electrode 54 has three beam-guiding holes having a large diameter. The intermediate electrode GM is a thick-plate electrode having three large beam-guiding holes. The sixth grid G6 comprises a thick-plate electrode 61, a thin-plate electrode 62 and two cup-shaped electrodes 63 and 64. The thick-plate electrode 61 has three beam-guiding holes. The thin-plate electrode 62 has three beam-guiding holes elongated in the inline direction. The cup-shaped electrodes 63 and 64 abut each other at their open ends. The convergence cup 90 is fastened to the bottom of the cup-shaped electrode 64.
A DC voltage of, for example, about 100 to 150V is applied to the cathodes KB, KG and KR. A modulation signal corresponding to an image is supplied also to the cathodes KB, KG and KR. The first grid G1 is connected to the ground. The second grid G2 and the fourth gird G4 are connected to each other in the tube. A DC voltage of about 600 to 800V is applied to the second and fourth grids G2 and G4. The cathodes KB, KG and KR and the first and second grids G1 and G2 compose a three-pole section for emitting electron beams and forming a crossover. The third grid G3 and the fifth grid G5 are connected to each other in the tube. A voltage of about 6 to 9V is applied to the third and fifth grids G3 and G5, serving as a focusing voltage. An anode voltage of about 25 to 30 kV is applied to the sixth grid G6.
The second grid G2 and the third grid G3 constitute a pre-focusing electron lens. The pre-focusing electron lens performs preliminary focusing on the electron beams emitted from the three-pole section. The third grid G3, fourth grid G4 and fifth grid G5 compose an auxiliary electron lens, which performs further preliminary focusing on the electron beams.
The resistor, provided near the electron gun assembly, applies a voltage to the intermediate grid GM. This voltage has a value almost halfway between the voltages applied to the fifth and sixth grids G5 and G6. In the electron gun assembly, the fifth grid G5, intermediate electrode GM and sixth grid G6 jointly form a main electron lens. The main electron lens focuses the electron beams finally on the phosphor screen of the color cathode ray tube that incorporates the electron gun assembly. The main electron lens is generally called "extended electric-field lens," because it is expanded by the intermediate electrode GM.
As shown in FIG. 2A, the axis of either hole for guiding a side beam, made in that end of the fifth grid G5 which oppose the intermediate electrode GM, is spaced by a distance Sg1 from the axis of the hole for guiding the center beam, made in that end. The axis of either hole for guiding a side beam, made in the intermediate electrode GM, is spaced by a distance Sg2 from the axis of the center beam. And the axis of either hole for guiding a side beam, made in that end of the sixth grid G6 which opposes the intermediate electrode GM, is spaced by a distances Sg3 from the axis of the hole for guiding the center beam made in that end of the sixth grid G6. The distances Sg1, Sg2 and Sg3 have the following relation:
Sg1.ltoreq.Sg2&lt;Sg3, or PA1 Sg1&lt;Sg2.ltoreq.Sg3 PA1 an electron gun assembly of inline type for emitting a center electron beam and a pair of side electron beams, which are traveled in the same horizontal plane; and PA1 a deflection yoke for generating magnetic fields for deflecting the three electron beams emitted from the electron gun assembly, thereby to scan a target with the three electron beams, PA1 the electron gun assembly comprising: PA1 Sg1&lt;Sg2.ltoreq.Sg3, or PA1 Sg1.ltoreq.Sg2&lt;Sg3 (wherein one of the distances Sg1, Sg2, and Sg3 is smaller than the distance Sg0 or all of the distances Sg1, Sg2, and Sg3 are smaller than the distance Sg0.) PA1 Sg1&lt;Sg2(1).ltoreq.Sg2(2).ltoreq.Sg3, or PA1 Sg1&lt;Sg2(1) and Sg2(2)&lt;Sg3, wherein at least one of the distances Sg1, Sg2(1), Sg2(2), Sg3 is smaller than the distance Sg0 or all of the distances Sg1, Sg2, Sg3 are smaller than the distance Sg0. PA1 an electron gun assembly of inline type for emitting a center electron beam and a pair of side electron beams, which are traveled in the same horizontal plane; and PA1 a deflection yoke generating magnetic fields for deflecting the three electron beams emitted from the electron gun assembly, thereby to scan a target with the three electron beams, PA1 the electron gun assembly comprising: PA1 an electron gun assembly of inline type for emitting a center electron beam and a pair of side electron beams, which have axes extending in the same horizontal plane; and PA1 a deflection yoke for deflecting the electron beams for generating magnetic fields for deflecting the three electron beams emitted from the electron gun assembly, thereby to scan a target with the three electron beams, PA1 the electron gun assembly comprising: PA1 Sg1&lt;Sg2(1).ltoreq.Sg2(2).ltoreq.Sg3, or PA1 Sg1&lt;Sg2(1) and Sg2(2)&lt;Sg3, wherein at least one of the distances Sg1, Sg2(1), Sg2(2), Sg3 is smaller than the distance Sg0 or all of the distances Sg1, Sg2, Sg3 are smaller than the distance Sg0, and the beam guiding holes of the first grid have a diameter smaller than the beam guiding holes of the third grid, the beam guiding holes of the third grid are smaller than the beam guiding holes of the fourth grid, and the beam guiding holes of the fourth grid are smaller than the beam guiding holes of the second grid.
Both side beams are, therefore, deflected toward the center beam, so that the three electron beams may converged at the center part of the phosphor screen. At the center part of the phosphor screen, however, the three electron beams are not converted perfectly. Rather, the electron gun assembly is so designed to convert the three electron beams either a little inadequately or excessively at the center of the phosphor screen, before the electron gun assembly is incorporated into a color cathode ray tube.
After the tube-up process, or once the assembly is set in the color cathode ray tube, the assembly is adjusted so that the two-pole convergence magnet, four-pole convergence magnet and six-pole convergence magnet, all provided around the neck of the tube, may finally convert the electron beams at the center of the phosphor screen. Thus, the difference in beam converging, resulting from the difference in the conditions under which gun assemblies have been manufactured is eliminated.
Before incorporated into the tube, the assembly may be designed such that the three electron beams are converged inadequately, like most electron gun assemblies. In this case, the assembly is so adjusted after the tube-up process that the side electron beams are deflected toward the center electron beam and incident in the main electron lens by means of the convergence magnets.
As shown in FIG. 3A, the side electron beams are applied from the beam-emitting section to the main electron lens (i.e., the fifth grid G5, intermediate electrode GM and sixth grid G6). Hence, the side electron beams travel through a high-aberration section in the case where they are deflected toward the center electron beam. As a result, the beam spot 11 that the side beam 6B forms on the phosphor screen has halo 10 as shown in FIG. 3B. As shown in FIG. 3B, the halo 10 is extended in the direction opposite to the center beam 6G in the inline plane. The same is true for the beam spot formed on the phosphor screen by the side beam 6R travelling on the other side of the center beam 6G. Thus, the two side beams 6B and 6R have halos extending in the opposite direction. Consequently, the image formed on the phosphor screen is deteriorated very much. In FIG. 3A, CM is a convergence magnet.